Crystalline alumina composites

Abstract

The adhesion of crystalline alumina to adhesives is enhanced by coating the surface of the alumina that is to be in contact with the adhesive, with a very thin coating of a siliceous material such as sputter coated silica.

What is claimed: 
     
       1. A composite comprising a crystalline alumina article adhesively bonded to a substrate, wherein at least a portion of the surface of said article that is adhesively bonded to said substrate comprises crystalline alumina having a thin adherent coating of a siliceous material, wherein said siliceous material consists essentially of silica or a glass containing at least 50 mol percent silica. 
     
     
       2. The composite of claim 1 wherein the adhesive bond between said coating of a siliceous material and the adhesive bonding said article to said substrate is enhanced by a silane coupling agent. 
     
     
       3. The composite of claim 1 or 2 wherein said crystalline alumina is crystalline alpha-alumina. 
     
     
       4. The composite of claim 1 or 2 wherein said siliceous material is silica. 
     
     
       5. The composite of claim 3 wherein said siliceous material is silica. 
     
     
       6. The composite of claim 1 or 2 wherein said article is an orthodontic bracket comprising a base member including a tooth contacting surface and a body member extending from said base member, said body member including walls defining an archwire groove. 
     
     
       7. The composite of claim 3 wherein said article is an orthodontic bracket comprising a base member including a tooth contacting surface and a body member extending from said base member, said body member including walls defining an archwire groove. 
     
     
       8. The composite of claim 2 wherein said article is an orthodontic bracket comprising a base member including a tooth contacting surface and a body member extending from said base member, said body member including walls defining an archwire groove. 
     
     
       9. The composite of claim 8 wherein said composite comprises an orthodontic bracket. 
     
     
       10. The composite of claim 2 wherein the adhesive is an epoxy resin and the silane coupling agent contains an amino group. 
     
     
       11. A method of producing a composite which comprises the steps of coating at least a portion of the surface of a crystalline alumina article with a thin adherent coating of a siliceous material, and then bonding said article to a substrate by adhesively bonding said surface having the siliceous coating to the substrate using an adhesive that has an adhesive affinity for said siliceous coating. 
     
     
       12. The method of claim 11 wherein said siliceous material is silica. 
     
     
       13. The method of claim 11 or 12 wherein the crystalline alumina is crystalline alpha-alumina. 
     
     
       14. The method of claim 11 or 12 wherein the adhesive bond between said adhesive and said siliceous coating is enhanced by the use of a silane coupling agent. 
     
     
       15. The method of claim 14 wherein the adhesive is an acrylic material and the silane coupling agent contains ethylenic unsaturation. 
     
     
       16. The method of claim 11 or 12 wherein said article is an orthodontic bracket comprising a base member including a tooth contacting surface and a body member extending from said base member, said body member including walls defining an archwire groove. 
     
     
       17. The method of claim 13 wherein said article is an orthodontic bracket comprising a base member including a tooth contacting surface and a body member extending from said base member, said body member including walls defining an archwire groove. 
     
     
       18. The method of claim 14 wherein said article is an orthodontic bracket comprising a base member including a tooth contacting surface and a body member extending from said base member, said body member including walls defining an archwire groove. 
     
     
       19. The method of claim 15 wherein said article is an orthodontic bracket comprising a base member including a tooth contacting surface and a body member extending from said base member, said body member including walls defining an archwire groove.